Method for applying mechanically sensitive layers to a substrate over a large area

ABSTRACT

A method is described for large-area application of at least two, for example, electroluminescent layers onto a substrate. In a process step A), spacer ( 5 ) is structured on the transparent substrate in such a way that, upon application of a second functional layer ( 11 ), contact between a first functional layer ( 10 ) already applied on the substrate and a part of a printing machine responsible for the transfer of the functional layers onto the substrate is avoided. In two other process steps B) and C), the first functional layer ( 10 ) and the second functional layer ( 15 ) are applied over a large area, for example, through large-area standard printing methods.

[0001] The so-called liquid crystal displays (LCDs) dominate the marketof the flat screen fields today. However, besides cost-effectivemanufacturing, low electrical uptake, low weight and low spacerequirements, the LCD technique also has severe disadvantages. LCDs donot emit themselves and therefore can be read easily or recognized onlywhen the environmental lighting conditions are especially favorable. Inmost cases, this requires back-lighting, but this again increases thethickness of the flat screen several times. In addition, the predominantpart of the electrical power uptake is then used for illumination and ahigher voltage is needed for the operation of the lamps or fluorescenttubes. This is produced mostly with the aid of voltage-up convertersfrom storage batteries. Another disadvantage is the highly limited angleof viewing of simple LCDs and the long switching times of individualpixels, which typically are in the range of a few milliseconds and arehighly temperature-dependent. The delayed appearance of the image isextremely disturbing, especially when used in vehicles or in videoapplications.

[0002] Since 1987, displays based on organic light emitting diodes(OLEDs) have become known. These consist in principle ofelectroluminescent organic layers, which are arranged between twoelectrodes. When an electric potential is applied to the electrodes,emission of light then occurs due to the recombination between electronsand “holes”, which are injected into the organic layer.

[0003] OLEDs do not exhibit the disadvantages mentioned above. Due toself-emission, the need for back-lighting is eliminated, which reducesthe space requirement and the electrical power uptake considerably. Theswitching times lie in the region of one microsecond and are onlyslightly temperature-dependent, which makes use for video applicationspossible. The reading angle is almost 180°. Polarization films, whichare necessary for LCDs, are mostly eliminated, so that greaterbrightness of the display elements can be achieved. Another advantage isthat flexible and nonplanar substrates can be utilized.

[0004] In the manufacture of OLEDs, low-molecular organic materials, forexample, hydroxyquinoline aluminum(III) salts can be used, which areapplied mostly by thermal evaporation onto a corresponding substrate.Displays based on this technology are already commercially availableand, at this time, are used mainly in automobile electronics. However,since the manufacture of these components requires numerous processsteps under high vacuum, this technology involves disadvantages due tohigh investment and maintenance costs, as well as relatively lowthroughput.

[0005] Therefore, an OLED technology was developed that uses polymers asorganic materials, which can be applied from a solution onto thesubstrate using wet chemical methods. The vacuum steps necessary forproducing the organic layers are eliminated with this technology. At thepresent time, the electroluminescent polymers are applied mostly withthe aid of a rotary centrifugal method. This method has a number ofdisadvantages:

[0006] The majority of the polymer solution (about 99%) is lostirrevocably, the centrifuging process takes a relatively long time(about 30 to 60 seconds) and, moreover, it is almost impossible to applyhomogeneous polymer layers onto large substrates.

[0007] In the OLEDs, frequently multilayer functional polymer layers areused that consist of, for example, hole transport polymers and emitterpolymers. It is known from publication EP 0 892 028 A2 that functionallayers can be applied into the window of a window layer with the aid ofa contactless ink-jet printing method, which defines the pixels.However, with the aid of this contactless printing method, multilayerfunctional layers can also be produced. However, using the ink-jetprinting method, smooth surfaces are very difficult to coathomogeneously. Moreover, ink-jet printing methods are verytime-consuming and thus costly.

[0008] A number of standard printing methods are known from publicationWO 99/07189, for example, a roll printing method, offset printingmethod, as well as screen printing method, for the application ofelectroluminescent polymers. These standard printing methods have thegreat advantage that, with them, functional layers can be applied ontolarge areas very rapidly and cost-effectively. However, problems arisewith these standard printing methods when two or more functional polymerlayers applied on top of one another or next to one another. In thiscase, the part of the printing device which is responsible for thetransfer of the functional layers, for example, the screen, thetemplate, the dabber or the roll, penetrates into the already appliedmechanically sensitive polymer layer and damages it. Among others, thepower of the OLED display produced in this way suffers, too, so that onemust expect a shortening of the life and nonhomogeneous illumination ofthe display.

[0009] The task of the invention is to provide a method for thepreparation of OLED displays with the aid of large-area standardprinting methods that can be used to apply mechanically sensitivepolymers onto a substrate, avoiding the disadvantages mentioned above.

[0010] This task is solved by a manufacturing method according to claim1. Advantageous embodiments of the manufacturing method are the objectsof the Subclaims.

[0011] In the manufacturing method according to the invention, spacersare applied onto a substrate in such a way that the part of the printingdevice that is responsible for the transfer of the functional layers,for example, the screens or printing rolls, can contact only the spacer,but not any other already-applied easily mechanically-damageable layers.Thus, it is possible to apply the spacers before the application of atleast two functional mechanically sensitive layers onto the substrate,First, the first functional layer can be applied, followed by theapplication of the spacer, and then the second functional layer isproduced. The method according to the invention includes the structuringof the spacer in a process step A) where, in at least two other processsteps B) and C) a first and a second functional layer are appliedwithout the first functional layer being damaged during the applicationof the second functional layer. Here, it is important that thestructuring of the spacer in process step A) be done before theapplication of the second functional layer (process step C)). The timesequence of steps A) and B) is interchangeable.

[0012] The spacers are advantageously structured in such a way thattheir maximum distance is smaller than the smallest horizontal dimensionof the part of the printer, which is responsible for the transfer of thefunctional layers onto the substrate. The printing roll can be preventedfrom falling between any peg-shaped spacers and, as a result, frompressing into the already applied functional layers.

[0013] The spacers can be structured, for example, in the form of pegsor strip-like partitions. In the case of strip-like partitions, it isadvantageous to structure these in such a way that they have anapproximate height of 0.1 to 100 μm, an approximate width of 0.3 to 300μm and an approximate distance from one another of 2 μm to about 10 mm.With these heights and distances of the spacers from one another,large-area functional layers can be applied with a number of large-areastandard printing methods, for example, gravure or letterpress methods,such as flexographic printing, planographic printing, such as offsetprinting and porous printing methods such as screen printing, withoutdamaging the already applied other functional layers. The approximatewidth of 0.3 to 300 μm in the case of spacers provides sufficientmechanical stability of the spacers so that they will not be damaged bythe part of the printing device which is responsible for the transfer ofthe functional layers.

[0014] For example, the spacers can be structured in such a way that apositive or negative photoresist is applied on a large area of thesubstrate to be printed, then illuminated through a mask and developed.The structured photoresist layer then forms the spacer. However, thespacers can also be applied onto the substrate by printing, for whichpurpose, for example, a polymer solution can be used.

[0015] Since the functional layers have no contact with the firstelectrode layer in the area of the spacer, these areas will not light uplater. For this reason, it is advantageous, in case of light radiationthrough a transparent substrate, and in the case of a transparent firstelectrode applied onto the substrate, to make the substrate matte on theside of the viewer, at least in partial areas. The matting is producedby small microscopic depressions in the surface. Each such depressionacts as a scattering center for the emitted light. Due to the diffusedistribution of the light and the related homogenization of the emittedradiation, the related homogenization of the emitted light can make thethin spacers almost “invisible” to the viewer of the finished display.If one uses, for example, glass plates as transparent substrates, thenthese can be roughened by sandblasting and thus made matte. The mattingcan be done at any time during the process according to the invention.

[0016] If the emission of light occurs through a second transparentelectrode applied onto the functional layers through a transparentcover, then advantageously, the cover which can be glass or plastic, forexample, can be matted.

[0017] The material from which the spacers are made is preferablyelectrically nonconducting, since otherwise the spacers could produceshort circuits between the electrode layers of the OLED displays.Moreover, the spacers should be chemically inert toward the functionalpolymers, so that the spacers cannot enter into any chemical reactionswith the polymers and thus change their function.

[0018] The method according to the invention will be explained belowwith the aid of a practical example, as well as several figures.

[0019]FIGS. 1A to 1F show a possible variation of a method according tothe invention, viewed from the top.

[0020]FIGS. 1H to 1P show another possible variation of a methodaccording to the invention, in cross-section.

[0021]FIGS. 2A to 2H show possible forms of the spacer.

[0022]FIG. 3 shows examples of the cross-sections of the spacer.

[0023]FIG. 4 shows a symbol to be printed.

[0024]FIGS. 1A to 1F explain an example of the method according to theinvention in a top view for large-area application of functional,electroluminescent layers which include, in addition to the necessaryprocess steps A), B) and C), a number of optional, additionaladvantageous process steps.

[0025] As already mentioned, in a process step A1), the side ofsubstrate 1 facing the viewer can be matted at least in partial areas,so that, due to the homogenized radiation of light, the spacers to beapplied later become quasi “invisible”.

[0026]FIG. 1A shows a possible process step A3) in which a firstelectrode layer 15A with an electrically connected first electrodeconnecting piece 15B and next to it a second electrode connecting piece20B are applied onto the transparent substrate 1 and then structured.For example, indium-tin oxide (ITO) is used as electrically conductingtransparent electrode material, which can be structured with liquid HBr.

[0027] In a next process step A2), as shown in FIG. 1B, a firstinsulating layer can be applied and then structured into the firststrip-like partitions 25. These partitions 25 border the large areawhere the first and second functional layers will be applied. Thesefirst strip-like partitions 25 have the advantage that they preventrunning of the functional layer during application. As a result of thepolymer solution running, during pressing the thickness of the polymerlayer would be reduced, especially at the outer pixels, which would leadto nonhomogeneous illumination and to a reduced life of the display.

[0028] Moreover, later, it is possible to provide a cover, for example,a plastic cap to the sensitive functional layer as well as to theoxidation-sensitive second electrode material located on top of it, thisplastic cap sealing these parts of the display tightly. Advantageously,the functional layers will not run into the areas of the transparentsubstrate 1 onto which the later cover is applied. Similarly, thoseregions of the first and second electrode connecting pieces 15B and 20B,which are introduced under the encapsulation, should not be covered byrunning functional polymers.

[0029] As a rule, the first strip-like partitions 25 consist of fourpartitions, of which always two partitions are transverse to the othertwo partitions and form a coherent partition structure, which delineateand define the region on which the functional layers should be applied.Furthermore, it is possible to surround these first four strip-likepartitions by other strip-like partitions 35. As a result of this, itbecomes possible that, during application of several functional layers,for example, the first functional layer is delineated by the firststrip-like partitions 25, where the second functional layer to beapplied is then delineated by the partition structure 35.

[0030] In contrast to spacers, which can also be produced in the form ofstrip-like partitions, the first partitions 25 delineate the areas of anOLED, which are printed on a large surface, so that even on a finisheddisplay, the function of these partitions can still be clearlyrecognized. On the other hand, the spacers are on the area of thedisplay onto which the functional layers are applied. In the case of afinished display, these spacers then are completely covered by thefunctional layers and then do not perform any obvious function anymore.

[0031]FIG. 1C shows the process step A) in which the spacers 5 areproduced in such a way that during later application of a secondfunctional layer, a contact between a first functional layer alreadylocated on the substrate and a part of a printing machine responsiblefor transferring the functional layer onto the substrate is avoided. Asalready mentioned, the spacers 5 can be structured in such a way that,for example, a photoresist is illuminated and developed through a mask.

[0032] Since, later on, a second electrode material is applied on alarge area, in process step A), the spacers 5 are advantageouslystructured in such a way that their regions, which are removed fartherfrom substrate 1, have a cross-section which becomes smaller, that is,show no overhanging edge form (see FIG. 3). This has the advantage thatthe metal film cannot be separated at spacers, which are structured insuch a way that the metal film therefore cannot be separated from therest of the second electrode material. These partition cross-sectionsare especially advantageous for those spacers 5 which completely includea part of the area that will be illuminated later. In all otherinterrupted partition structures, complete tearing off of the metal filmis not to be feared.

[0033]FIG. 1D shows process steps B) and C), in which the first andsecond functional layer are applied over a large area. Advantageously,these layers 10 and 11 are applied using large-area printing methods,for example, planographic printing methods, such as offset printing, padprinting, porous printing, such as screen printing or stencil printingor also letterpress printing and gravure printing, such as flexographicprinting.

[0034] It is shown in FIG. 1E how, in a next process step D) a secondelectrode layer 20A, which contacts the second electrode connectingpiece 20B, is applied over a large area on the functional layers 10 and11. For example, it is possible to evaporate the second electrode layerover a large area as a metal film, for example, aluminum or magnesium,using a shadow mask.

[0035] In the next process step E), as shown in FIG. 1F, a cover 30 canbe applied onto the area of functional layers 10 and 11, the secondelectrode layer 20A and one end each of the first and second electrodeconnecting piece 15B and 20B. This cover 30 can be, for example, aplastic.

[0036]FIGS. 1H to 1P explain another example of the method according tothe invention for application of the functional electroluminescentlayers of large area, using the example of a rotating roller printingmethod.

[0037]FIG. 1H shows in cross-section the schematic structure of asubstrate 1 with a first electrode layer 15A and spacers 5 before thebeginning of the printing process (process steps B) and C)). The spacers5 are produced after the application of the first electrode layer 15Aonto substrate 1 in the first process step A) of the method according tothe invention.

[0038]FIG. 1I shows the arrangement in cross-section during the secondprocess step B). A rotating print roll 7 transfers the first functionallayer 10A in the printable (liquid) state onto substrate 1.

[0039]FIG. 1J shows the first functional layers 10A after process stepB) before drying. Since the layer thickness of the functional layer, forexample, 5 μm, is usually larger than the maximum height of the spacer,which can be 2 μm, the raised parts of the spacer are completely coveredby the functional layers, so that a flat surface is produced on thesubstrate.

[0040]FIG. 1K shows the first printed functional layer 10 after drying.Since the printable functional layers contain a very large amount ofsolvent (up to 99%), these layers shrink considerably during the dryingprocess due to the evaporation of the solvent. Thus, the layer thicknessof an electroluminescent layer decreases during drying, for example,from 5 μm to about 75 nm. As a result of this, the spacers will behigher than the already applied functional layer and thus their functionduring the application of the second functional layer in process step C)can be exhibited.

[0041]FIG. 1L shows the large-area printing of the second functionallayer 11A in the liquid state during process step C). Here, the spacersprevent print roll 7 from coming too near the first functional layer anddamaging it. Since, as already mentioned in FIG. 1J, the thickness ofthe second functional layer on the print roll is greater than themaximum height of the spacers, transfer of the functional layer from theprint roll to the substrate is still possible.

[0042]FIG. 1M shows the second functional layer 11A directly afterprocess step C) before drying. Analogously to that shown in FIG. 1J, aflat surface is produced, since the spacer is completely covered.

[0043] After drying of the second functional layer, as shown in FIG. 1N,the elevations of the spacers protrude again. As a result, it becomespossible, with the method according to the invention, to print more thantwo mechanically sensitive functional layers on top of one another.

[0044]FIG. 1O shows how the second electrode layer 20A is applied ontothe functional layers over a large area. This can be achieved, forexample, by evaporating a metal film over a large area through a shadowmask.

[0045]FIG. 1P shows how a cover 30 is applied so that it covers thesecond electrode layer and the functional layers. It can consist, forexample, of plastic or glass. The arrows show schematically thedirection in which the electroluminescent light can be radiated throughthe transparent substrate 1 and the transparent first electrode layer15A. Only those areas of the two functional layers 10 and 11 will emitelectroluminescence, which are in contact with both electrode layers. Inthe region of spacers 5, there is no contact of the electroluminescentlayers with the first electrode layer 15A, so that these areas do notemit any light.

[0046] The following FIGS. 2A to 2H show possible partition structuresof the spacers in a top view. However, in principle, other embodimentsof the spacers besides partition structures can also be conceived, forexample, pegs on the surface to be printed. Since the spacers can stillbe seen under certain circumstances on the finished display, theesthetic aspect in the design of the spacers may also play a role.

[0047]FIG. 2A shows spacers in the form of strip-like partitionsarranged parallel to one another. FIG. 2B shows a checkerboardarrangement of strip-like partitions. FIG. 2C shows a honeycombarrangement of strip-like partitions as spacers 5. FIG. 2D showsinterrupted, strip-like partitions which are arranged displaced withrespect to one another and are parallel to one another. FIG. 2E showsstrip-like partitions which are arranged transversely on the substrate.FIG. 2F shows strip-like, wavy partitions. FIG. 2G shows circularstrip-like partitions, while FIG. 2H shows strip-like, interruptedpartitions running parallel to one another.

[0048]FIG. 3 shows possible cross-sections of the strip-like partitionsas spacers 5. In the areas which are farther removed from the substrate,they have a cross-section becoming smaller, so that a metal film to beapplied later on to these types of partitions cannot tear off.

[0049] For a whole series of display applications, for example, forhandys or cockpits, so-called icon bars or symbol strips are necessary.These symbols are typically embedded into the partition structures.

[0050] If the illuminated surfaces of the symbols occupy a larger area,for example, in the case of the symbol in the form of a house shown inFIG. 4, where the black areas designated with 40 should light up and theareas designated with 45 should not light up, it is expedient to fillthe illuminating surfaces 40 with spacers 5, so that large-area printingof these areas becomes possible.

[0051] The method according to the invention can be also employed inpassive matrix displays, whereby, in this case, the first and secondelectrode layers are structured to strip-like electrode stripsperpendicular to one another and the matrix of individually controllablepixels is structured. In the case of passive matrix displays, frequentlystrip-like partitions are structured which are perpendicular to thefirst electrode strip and on which a later, second electrode layerapplied over a large surface is torn off so that the second electrodestrips can be formed. These partitions can, for example, be modifiedwith respect to one another regarding their size and distance, so that,at the same time, they can also function as spacers 5.

[0052] The method according to the invention is not limited to thepractical examples specifically described here. Especially, with theinvention, other mechanically sensitive layers can be produced on top ofone another without damage, with a predetermined layer thickness andwith high layer thickness homogeneity. Naturally, other variations arealso within the framework of the invention, especially regarding thematerials used for the spacers as well as their structure.

1-14. (Canceled)
 15. A method for application of layers on a substrate,comprising: forming spacers on a substrate; forming a first functionallayer on the substrate so that a first portion of the first functionallayer is between the spacers; and printing a second functional layer onthe first functional layer with a printing device, wherein the spacersprevent contact between the first portion of the first functional layerand a part of the printing device responsible for printing the secondfunctional layer.
 16. The method of claim 15, wherein: forming thespacers includes forming the spacers to have a maximum distance betweenadjacent spacers, the maximum distance being less than a smallestdimension of the part of the printing device responsible for printingthe second functional layer.
 17. The method of claim 15, wherein:printing the second functional layer includes contacting a portion ofthe first layer that is on the spacers with the part of the printingdevice responsible for printing the second functional layer; forming thespacers includes forming each spacer at a distance from an adjacentspacer sufficient to prevent the part of the printing device responsiblefor printing the second functional layer from contacting the firstportion of the first functional layer.
 18. The method of claim 15,wherein: forming the spacers includes structuring the spacers intostrip-like partitions.
 19. The method of claim 18, wherein: forming thespacers includes structuring the spacers to have a height between about0.1 and 100 microns, a width between about 0.3 and 300 microns and adistance between each spacer of between about 2 microns and 10millimeters.
 20. The method of claim 15, wherein: forming spacers on asubstrate includes forming spacers on a matted substrate; forming thefirst functional layer includes forming a first electroluminescent layeronto a transparent substrate; and printing the second functional layerincludes printing a second electroluminescent layer.
 21. The method ofclaim 15, wherein the first functional layer is formed on a firstsurface of the substrate, the method further comprising: sandblasting asecond surface of the substrate.
 22. The method of claim 15, wherein:forming the spacers includes exposing a photoresist through a mask anddeveloping the photoresist.
 23. The method of claim 15, wherein: formingthe spacers includes printing.
 24. The method of claim 15, wherein:forming the spacers includes structuring the spacers to have a taperedcross-section that is wider at a portion of the spacer that is closestto the substrate than a portion that is further from the substrate. 25.The method of claim 15, further comprising: forming a insulating layersuch that the insulating layer is in strip-like partitions, wherein thestrip-like partitions serve to delineate boundaries of the first andsecond functional layers.
 26. The method of claim 15, wherein: formingthe first functional layer includes applying the first functional layerwith a large-area printing process.
 27. The method of claim 15, wherein:forming the second functional layer includes applying the secondfunctional layer with a large-area printing process.
 28. The method ofclaim 15, wherein: forming the first functional layer includes at leastone printing method from the group consisting of planographic printing,gravure printing, letterpress printing, screen printing and stencilprinting.
 29. The method of claim 15, wherein: printing the secondfunctional layer includes at least one printing method from the groupconsisting of planographic printing, gravure printing, letterpressprinting, screen printing and stencil printing.
 30. The method of claim15, further comprising: forming a first electrode layer on the substrateprior to forming the first functional layer.
 31. The method of claim 30,further comprising: forming a second electrode layer onto the secondfunctional layer.
 32. The method of claim 31, further comprising:forming a first electrode connecting piece and a second electrodeconnecting piece on the substrate, wherein the first electrodeconnecting piece electrically contacts the first electrode layer andforming the second electrode layer includes forming the second electrodelayer so that the second electrode layer electrically contacts thesecond electrode connecting piece; and applying a cover onto an areaincluding the first and second functional layers, the second electrodelayer and an end of the first and second electrode connecting pieces.33. A method for applying layers on a substrate to form a light emittingdevice, comprising: forming a first electrode layer on a substrate,wherein the first electrode layer includes a first electrode connectingpiece; forming spacers on the substrate; forming a firstelectroluminescent layer on the substrate, wherein a first portion ofthe first electroluminescent layer is between the spacers; printing asecond electroluminescent layer on the first electroluminescent layerwith a printing device, wherein the spacers prevent contact between thefirst portion of the first functional layer and a part of the printingdevice responsible for printing the second functional layer; forming asecond electrode layer on the second electroluminescent layer; forming asecond electrode connecting piece that is in electrical contact with thesecond electrode layer; and encapsulating the first and second electrodelayers, the spacers, and the first and second electroluminescent layerswith an encapsulation so that at least one end of the first and secondelectrode connecting pieces are free from the encapsulation.